In the offshore oil industry, floating structures are used in areas where deep water causes a jacket fixed to the sea floor to be too expensive to realize a sufficient economic return, even for large oil reserves. Accordingly, floating structures, such as SPAR's and semi-submersibles that are moored in place with multiple anchors, or dynamically positioned vessels are used.
Each structure has its advantages and disadvantages.
A need has existed for a vessel with a larger deck area than conventional spars.
A need has existed for a semi-submersible with improved vertical motion that can be built quickly with fewer components than other semi-submersibles.
Traditional drilling semi-submersibles require the use of seafloor Blow Out Preventers which are disconnected and retrieved to the surface prior to hurricane abandonment. The riser system is not designed to sustain the vertical motions of the semi-submersible during the hurricane. The safety and environmental implications of this system should be obvious. In deepwater, the time and complexity of the operations required to retrieve the riser prior to abandonment is significantly more important to the overall productivity of drilling operations than it had been in shallower water. Also, the complexity of the risers required to accomplish this is significantly greater. The productivity of the drilling in deepwater has been significantly adversely affected by the complexity of these operations and the economics of deepwater exploration and production development systems have been hurt by these productivity problems.
A need has existed for a semi-submersible that can be built in components in a modular manner, in one yard or in multiple yards that are at different geographic locations.
A need has existed for a semi-submersible design which has sufficiently small vertical motions that dry tree production and drilling risers can be used. The deep draft required to accomplish these small motions requires that the semi-submersible be built horizontally and float in a shallow draft of less than 40 feet.
A need has existed for a semi-submersible that is unconditionally stable.
A need has existed for a semi-submersible with sufficient emergency ballast to restore full design draft and trim.
The present embodiments meet these needs.
The present embodiments are detailed below with reference to the listed Figures.